With enterprises deploying wireless local area networks (WLAN) for a mobile workforce, new applications based on localization of assets and people using these wireless LANs are also taking hold. Significant increases in efficiency can potentially be realized by tracking high value assets using Wi-Fi tags in several environments including hospitals, university campus buildings and office buildings. Tracking building occupants such as patients in a hospital or employees and visitors in large office buildings enable various new services, improved productivity and safety.
Recently, localization techniques of tracked assets using wireless LANs have been proposed. Localization using WLANs is typically performed based on measurements of strength of signals received from the access points at the tag or by measuring the strength of the signals received from the tag at a few access points. Time delay of arrival is also sometimes used in location determination. Measurements from multiple access points in the neighborhood of the tag are used in a triangulation algorithm involving the known locations of the access points themselves to pin point the location of the tag.
A critical requirement for all localization algorithms is accurate knowledge of the location of the access points themselves. The location engine associated with a localization application uses a database that maps access points to their physical locations. However, for a variety of reasons there could be errors in the locations of the access points in the database. For example, at the deployment phase the location of an access point could be incorrectly entered into the database, or an access point might be moved subsequently without an update to the location database.
Thus, errors in location information associated with access points impart further errors within the context of localization techniques such as those associated with asset tracking applications.
Unfortunately, the correction of location errors by determining locations via triangulation is limited to those network configurations where there are a sufficient number of neighborhood nodes or access points to enable useful triangulation determinations. Many network installations simply do not provide a sufficiently node density to allow this technique.